1. Field of the Invention
The invention relates to a cutting tip for removal of metal during the processing of metal parts, such as, shafts, axles, etc. Particularly, it pertains to cutting tips for case-hardened and quenched and tempered steel, preferably for use at cutting speeds greater than 500 m/min, consisting of aluminum oxide with additions of zirconium oxide and sintered at a high temperature.
2. Description of the Prior Art
In recent decades, cutting tips based on aluminum oxide have proven themselves in an outstanding manner for the machining of metals. Thus, of the cutting materials available, these cutting tips have found steadily increasing use especially for machining operations at high cutting speeds which result in high temperatures. Aluminum oxide possesses a certain brittleness which decreases the life of the cutting edges of the cutting tips. Thus, such tips are not entirely satisfactory and in spite of the great hardness and wear resistance of the aluminum oxide cutting tips, efforts are still being made to further improve this material.
Quite a number of proposals have therefore already been made for making the aluminum oxide based, relatively brittle cutting tips more ductile by means of additives, i.e., in order to increase their ultimate breaking strength. Such additives may consist of metals which lead to the so-called "cermets". Additions of metal carbides, nitrides and borides, such as, for example, titanium carbide, which particularly increase the wear resistance, have proven to be valuable.
An older proposal disclosed in German Auslegeschrift No. 23 07 654 suggests using zirconium oxide as a material for cutting tips. This zirconium oxide is partially stabilized and has a cubic phase content of 75-95%. In German Offenlegungsschrift No. 27 41 295, this suggestion is taken up once again with the variation that 0.5 to 35 weight percent of the partially stabilized zirconium oxide is intercalated in a matrix of .alpha.-aluminum oxide. This provides an increase in the shape-stability of the cutting tips. Due to the relatively high stabilizer content, i.e., 4 weight percent of calcium oxide, the heat resistance of these cutting tips is decreased to such an extent that their performance at high cutting speeds is less than even that of a pure aluminum oxide ceramic.
The problems associated with these aluminum oxide cutting ceramics containing additives generally arise from the fact that the desired effect, for example, the prevention of brittleness, is too small if the amount of additive is insufficient and that the heat stability at the temperatures encountered at high cutting speeds is reduced as the amount of additive is increased.